Of the many previous studies related to hormone metabolism in patients with carcinoma of the breast, the "Bulbrook Discriminant" is, in my opinion, the only reported abnormality that has withstood the test of time. For the present, this abnormality of androgen metabolism represents an unexplained oddity and offers no insight into the hormonal environment of patients that develop breast cancer. Most other studies of steroid excretion have suffered from methodological inadequacies, particularly those related to estrogen metabolism. In recent years, major advances in steroid methodology have occurred. The application of radioimmunoassay methods to steroidal analysis has permitted accurate estimations of androgen and estrogen blood levels in normal and abnormal states. By coupling these measurements with constant infusion methods, it is now possible to estimate blood production rates and interconversion rates of the various steroidal hormones. This proposed study will re-investigate the hormonal environment of women who develop carcinoma of the breast. We will measure blood production rates of androgens and estrogens and the conversion of circulating androgens to estrogens. From these data, we will be able to determine: 1.)how much testosterone and androstenedione are produced daily, 2.) how much of these are converted to estradiol and estrone respectively in their peripheral metabolism, 3.) estrone and estradiol production rates, and 4.) how much of the daily production rates of estrone and estradiol comes from circulating androgens. With this approach it might be possible to define abnormalities in androgen and/or estrogen metabolism in women with carcinoma of the breast.